Glaucoma
Glaucoma is a disease that affects over 60 million people worldwide, or about 1-2% of the population. The disease is typically characterized by an elevation in eye pressure, known as the intraocular pressure, that causes pathological changes in the optic nerve which if left untreated can cause blindness. The increased intraocular pressure is generally caused by a resistance to drainage of aqueous humor or fluid from the eye.
Aqueous humor is a clear, colourless fluid that is continuously replenished by the ciliary body in the eye and then ultimately exits the eye through the trabecular meshwork. The trabecular meshwork extends circumferentially around the eye in the anterior chamber angle and feeds outwardly into a narrow circumferential passageway generally surrounding the exterior border of the trabecular meshwork, known as Schlemm's canal. From Schlemm's canal, aqueous humor empties into aqueous collector channels or veins positioned around, and radially extending from, Schlemm's canal. Pressure within the eye is determined by a balance between the production of aqueous humor and its exit through the trabecular meshwork.
Referring to FIG. 1, a cross-section of an eye 110 is illustrated to show the relative anatomy of Schlemm's canal 120, trabecular meshwork 130, iris 175, and anterior chamber 140. Anterior chamber 140 is bound anteriorly by cornea 180 which is connected on its periphery to sclera 185 which is a tough fibrous tissue forming the white shell of eye 110. Trabecular meshwork 130 is located on the outer periphery of anterior chamber 140 and extends 360 degrees circumferentially around anterior chamber 140 with Schlemm's canal 120 also extending 360 degrees circumferentially around the outer peripheral surface of trabecular meshwork 130.
Anterior chamber 140 of eye 110 is filled with aqueous humor which is produced by ciliary body 160 to ultimately exit eye 110 through trabecular meshwork 130. In a normal eye 110, aqueous humor passes through trabecular meshwork 130 into Schlemm's canal 120 and thereafter through a plurality of aqueous veins 170, which merge with blood-carrying veins (not shown), and into systemic venous circulation. Glaucoma is characterized by an excessive buildup of aqueous humor, which leads to an increase in intraocular pressure that is distributed relatively uniformly throughout eye 110. Resistance to flow in trabecular meshwork 130 and/or Schlemm's canal 120 can cause decreased flow of aqueous humor out of the eye 110 and increased intraocular pressure.
Treatment Methods
Treatments that reduce intraocular pressure can slow or stop progressive loss of vision associated with some forms of glaucoma and such treatments are currently the primary therapy for glaucoma. A number of treatment methods are currently used for reducing intraocular pressure to treat glaucoma including medication, laser therapies and various forms of surgery. Drug therapy includes topical ophthalmic drops or oral medications that either reduce the production or increase the outflow of aqueous humor. When medical and laser therapy fail, however, more invasive surgical therapy is typically used.
Surgical Techniques
Surgical techniques for treating glaucoma generally involve improving aqueous outflow. Trabeculectomy, a procedure which is widely practiced, involves microsurgical dissection to mechanically create a new drainage pathway for aqueous humor to drain, by removing a portion of sclera and trabecular meshwork at the drainage angle. Trabeculectomy, however, carries the risk of blockage of the surgically-created opening through scarring or other mechanisms, and has been found to have limited long-term success. Furthermore, Trabeculectomy surgery is associated with serious, potentially blinding complications.
Alternative surgical procedures to Trabeculectomy include tube shunt surgeries, non-penetrating Trabeculectomy and Viscocanalostomy. These procedures are invasive as they are “ab externo” (from the outside of the eye). Tube shunt surgeries involve significant extraocular and intraocular surgery with significant risk of surgical complications, as well as the long term risk of failure from scarring. In the case of viscocanalostomy and non-penetrating Trabeculectomy, the procedures involve making a deep incision into sclera, and creating a scleral flap to expose Schlemm's canal 120 for cannulation and dilation. Due to the delicate nature of these ab-externo approaches, they are difficult to execute. Due to the invasiveness of such procedures and the difficulty of successfully accessing the small diameter of Schlemm's canal 120 from the outside of the eye, “ab interno” techniques have been described for delivering ocular devices and compositions into Schlemm's canal 120 through trabecular meshwork 130 from the inside of eye 110.
In glaucoma, trabecular meshwork resistance creates increased intraocular pressure. Current minimally invasive glaucoma surgery (MIGS) techniques, such as iStent, Hydrus, and Trabectome, bypass trabecular meshwork 130 to reduce the intraocular pressure.
Diagnostic Systems
Optical Coherence Tomography
Tomography is a technique for displaying a representation of a cross section through a human body or other solid object using X-rays or ultrasound. Optical coherence tomography (OCT) is an established medical imaging technique that uses light to capture micrometer-resolution, three-dimensional images from within optical scattering media, such as biological tissue. OCT is based on low-coherence interferometry, typically employing near-infrared light. The use of relatively long wavelength light allows it to penetrate into the scattering medium.
Optical Coherence Tomography Angiography
Angiography is the examination by X-ray of blood or lymph vessels, carried out after introduction of a radiopaque substance. OCT Angiography (OCT-A), is the most important OCT technology developed in recent years. OCT-A detects the motion of red blood cells as intrinsic contrast, and therefore does not require the injection of extrinsic contrast dye, such as with fluorescein angiography or Indocyanine Green (ICG) angiography. This no-injection, dye-free technology is capable of three-dimensional imaging of capillary dropout or pathologic vessel growth in the leading cause of blindness: age-related macular degeneration, diabetic retinopathy, and glaucoma. The three-dimensional nature of OCT-A allows the segmentation of retinal and choroidal layers into distinct “slabs” for en face flow projection images that separately visualizes retinal and choroidal circulations, as well as abnormal choroidal neovascularization in the outer retina and retinal neovascularization in the vitreous space.
Multiple approaches for OCT-A have been developed. These include amplitude-based, phased-based, or combined amplitude/phase variance-based methods. Furthermore, new software algorithms have been developed which allow existing OCT hardware to perform OCT-A. These methods use either Doppler shift or variations in speckle pattern caused by moving red blood cells to detect both transverse and axial flow. These methods have become practical now because the high speed of Fourier-domain OCT allows multiple cross-sectional images to be obtained at the same location in very quick succession to detect relative motion in voxels contain blood flow. Both varieties of Fourier-domain OCT: spectral (a.k.a. spectral-domain or spectrometer-based) or swept-source, could be used. Three-dimensional volumetric OCT-A can be obtained in seconds. Subsequent processing allows the visualization of vascular networks down to the capillary level in both the retinal and choroidal circulations. Because of the high axial resolution of OCT, the retinal circulation could be further subdivided into the superficial and deep plexus as well as abnormal neovascularization into the vitreous space. The choroidal circulation could be subdivided into the choriocapillaris, the deeper choroid, and abnormal neovascularization above Bruch's membrane and into the retina. Anterior segment OCT-A of the episcleral space can also differentiate between aqueous veins from episcleral and conjunctival vasculature.
Laser Technologies
Types of laser of interest to eye surgery include excimer and femtosecond types of laser. An excimer laser, is a form of ultraviolet laser which is commonly used in the production of microelectronic devices, eye surgery, and micromachining. A femtosecond laser uses near-infrared wavelength light, which allows the light to be focused at a micron spot size, accurate within 5 microns in the anterior segment of the eye. Femtosecond laser has ultra short pulses (10−15 seconds, or a femtosecond hence the name) which advantageously eliminates collateral damage of surrounding tissues, when used in eye surgery.
Known Art
U.S. Patent Publication No. 2012/0283557 A1 to Berlin, discloses a method of creating and maintaining an opening in the trabecular meshwork of a patient's eye to conduct fluid from the anterior chamber to Schlemm's canal of the eye by applying laser pulses to form at least one of a drain channel or a humor outflow opening, wherein Schlemm's canal is detected optically or by OCT.
Nakamura H, Liu Y, Witt T E, et al. Femtosecond laser photodisruption of primate trabecular meshwork: an ex vivo study. Inv Ophthal Vis Sci 2009:1198-1204, studied the use of femtosecond laser for photodisruption of the primate trabecular meshwork ex vivo using a manually operated goniolens with direct visualization.
A similar procedure to the one studied by Nakamura, but without the use of femtosecond laser, is Gonioscopy Assisted Transluminal Trabeculectomy (GATT). Gonioscopy is an eye examination of the anterior chamber between the cornea and the iris to determine whether the drainage angle is open or closed. The GATT procedure is performed via micro-incisions in the cornea. An incision about 1.0 mm in size is made in the periphery of the cornea through which the surgery is completed. After entering the eye, the surgical procedure involves cutting through trabecular meshwork 130, cannulating Schlemm's canal 120 in 360 degrees, and unroofing Schlemm's canal 120. GATT reduces intraocular pressure by restoring the trabeculo-canalicular outflow pathway. GATT increases the flow of aqueous humor from the anterior chamber, directly into and around Schlemm's canal, and out through the collector channels. GATT achieves mean post-op intraocular pressure of 15.7 mmHg at 12 months in humans. However, GATT has a steep learning curve and sometimes it is not possible to thread the full 360 degrees of Schlemm's canal, which impedes its adoption by cataract surgeons and even many fellowship trained glaucoma surgeons.
TRAB360 is a similar surgical procedure to GATT. The TRAB360 surgical instrument is a “trabeculotome”; a non-powered instrument intended for the manual cutting of trabecular meshwork 130. TRAB360 can be used to mechanically cut up to 360 degrees of trabecular meshwork 130.
Selective Laser Trabeculoplasty (SLT), is a form of laser surgery that is used to lower intraocular pressure in glaucoma. Laser energy is applied to the drainage tissue in the eye. This starts a chemical and biological change in the tissue that results in better drainage of fluid through the drain and out of the eye. This eventually results in lowering of intraocular pressure. It may take 1-3 months for the results to appear.
It is an object of this invention to provide a novel system for the diagnosis and treatment of glaucoma by reducing intraocular pressure.